US Defense Secretary Jim Mattis' visit to Kiev represents an opportunity for the United States to provide lethal assistance to Ukraine, Senator John McCain said in statement.

"Secretary Mattis's visit to Kiev provides yet another opportunity for the United States to correct its policy toward Ukraine and provide the lethal defensive assistance the country needs to defend its sovereignty and territorial integrity," McCain said on Wednesday.

McCain said Ukraine would need lethal assistance in order to deter "Russian aggression" and achieve a peaceful resolution to the conflict.

"Raising the cost of aggression may help to change [President] Vladimir Putin's calculus, pressure Russia to fully comply with the Minsk agreements, and, ultimately, create more stable security conditions on the ground that are essential for peace," McCain added.

The senator said President Donald Trump took a first "significant step" deterring Russian aggression by signing new US sanctions into law.

"Changing US policy to provide lethal defensive assistance to Ukraine would be another step in the right direction – sending a strong signal that the United States will stand by the sovereign right of its allies and partners to choose their own future," McCain said.

Russia has repeatedly said that supplying weapons to Ukraine would not contribute to the settlement of the Ukrainian crisis, nor to the implementation of the ceasefire and might be perceived by Kiev as encouragement to take further military action.

Kiev launched a military operation in the east of Ukraine in 2014, after local residents refused to recognize the new government that came to power. A ceasefire agreement was reached in Minsk in 2015, brokered by the leaders of the Normandy Four group (Russia, France, Germany, Ukraine) but the situation has remained tense.